1. Field of the Invention
The present invention relates generally to a method for determining positive and negative emotional states by electroencephalogram (hereinafter referred to as an EEG). More particularly, it relates to a method for determining positive and negative emotional states by using that a relative power in a subband of a specific frequency band increases or decreases with the lapse of time.
2. Description of the Prior Art
In recent years, for a human being comfortable life, the information about a human being emotional state as a response to a peripheral environment has been requested to a product development research. Accordingly, a technique for estimating a human being response (i.e., emotional state) for the peripheral environment is required thereto.
To achieve the above technique, an EEG analysis method has been developed. The EEG analysis method discriminates between a pleasant emotion and a bad (unpleasant) emotion of human by using the EEG, which is applied to both a human's taste research and a product development.
There are two kinds of methods for analyzing the EEG, i.e., a linear analysis method such as a Fourier transform and a nonlinear analysis method such as a correlation dimension estimation.
The Fourier transform can obtain the information for a specific frequency component such as .alpha.-wave (8-13 Hz) and .beta.-wave (14-30 Hz) extensively studied. The correlation dimension estimation is used to determine whether or not EEG time series are chaos signals.
Since a conventional EEG analysis method uses all data of a response usually time (30 seconds-1 minute) for a stimulus, it is difficult to perform a real-time processing.
Also, the conventional EEG analysis method cannot be applied to a nonstationary EEG having a large variation in the course of time. Since the conventional EEG analysis method needs a reference line for comparing a present state with another state, it should measure EEG generated when no stimulus is applied to the human.
The conventional method for determining positive and negative emotional states can enhance an accuracy of a discrimination by analyzing a physiological signal (such as an electrocardiogram (ECG), a peripheral blood pressure, a galvanic skin resistance and a person's face expression) as well as the EEG. However, the user feels inconvenient in using the conventional method as a man-machine interface.